Molecular beam epitaxy consists of propelling atoms or molecules to the surface of a substrate in a very strong vacuum to avoid any interaction on the course of travel and minimize the contamination that stems from the residual gases of the vacuum. The molecules are produced by heating and evaporation under vacuum (circa 10−10 Torr) in a cell communicating with the epitaxy chamber. The materials used in epitaxy can be of a different nature and exist in solid, liquid or gaseous form. They are the constitutive elements of the semiconductor alloys called “compounds” (semiconductor compounds), i.e., formed by a minimum of two simple chemical elements, for example, gallium and nitrogen for GaN or gallium nitride, gallium, nitrogen and arsenic for GaAsN. There can be present materials for doping semiconductor compounds, e.g., silicon and beryllium for n or p doping of GaAs. There is described in the state of the art in U.S. Pat. No. 4,424,104 epitaxy equipment comprising an evaporation source closed by a grill.